I don't recall ever having heard of those events
My nuclear engineering courses were in 1969 when I was a senior. I'm thinking this might not have been made public at the time. As part of one of my classes we went to the Enrico Fermi 1 plant at Detroit Edison. It was a liquid sodium cooled breeder reactor that was Three Mile Island 2 on a small scale. The reactor was well on the way to critical and had melted some of the core when they managed to shut it down.
The "cause" was an undocumented modification to the core. Unlike TMI the operators followed procedures and the unit shut down as designed. It ultimately was repaired and refueled---but never reached full power and has long ago been deactivated.
"A pessimist sees the difficulty in every opportunity, an optimist sees the opportunity in every difficulty” ---Sir Winston Churchill
"Political extremism involves two prime ingredients: an excessively simple diagnosis of the world's ills, and a conviction that there are identifiable villains back of it all." ---John W. Gardner
“You can’t go back and change the beginning, but you can start where you are and change the ending.” ---C. S. Lewis